With the development of mobile telecommunications technologies, a multimode base station, that is, a base station capable of supporting a plurality of radio access technologies at the same time, has appeared. For example, a base station that is capable of supporting the two RATs, GSM (Global System for Mobile Communications; global system for mobile communications) and UMTS (Universal Mobile Telecommunications System; universal mobile telecommunications system) at the same time is called a GU dual-mode base station.
One solution of a multimode base station is superimposing boards of different standards to form a multimode base station. Taking a GU dual-mode base station as an example for illustration, a BBU (Base Band Unit; baseband unit) includes main control boards of various standards and boards that are of various standards and provide a CPRI interface (Common Public Radio Interface, common public radio interface). The board that provides a CPRI interface may be integrated with the main control board (such as the GSM standard), or it may be integrated with a service processing board (such as the UMTS standard).
As the radio frequency module of a multimode base station supports various standards, the system clock of a multimode radio frequency module must be synchronized with the main control system clocks of the two standards. Otherwise, the CPRI interface may experience problems, such as out-of-synchronization and malfunction of the intermediate radio frequency processing part.
Therefore, in a multimode base station, the synchronization of system clocks (or timing loop) of different standards is required.